LUCENE-5897, LUCENE-5400: change JFlex-generated source munging so that zzRefill() doesn't call Reader.read(buffer,start,len) with len=0

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_9@1625586 13f79535-47bb-0310-9956-ffa450edef68